This application is based upon and claims priority from prior European Patent Application No. 01-830275.2, filed Apr. 27, 2001, the entire disclosure of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to electronic circuits, and more specifically to a current reference circuit for low supply voltages such as a 1V supply voltage.
2. Description of Related Art
It is known to a person of ordinary skill in the relevant art that analog electronic circuitry needs current reference circuits and voltage reference circuits.
These current reference circuits have to be insensitive to the thermal changes and insensitive to the supply voltage oscillations.
Usually a bandgap voltage circuit is a way to generate the current reference.
However, if the bandgap voltage circuits do not work correctly, for example because the supply voltage decreases under a prefixed value, or because the supply voltage presents excessive oscillations or because the supply voltage is not stable in temperature, then the current reference circuits do not work correctly.
Particularly, in the case in which the voltage supply decreases under a threshold voltage value, for example under 1.5V, the voltage reference circuit cannot provide a stable reference voltage and, therefore, the current reference circuit cannot generate a stable current reference.
In view of these drawbacks, it is an object of the present invention to overcome the above-mentioned drawbacks and to provide a current reference circuit that is able to provide a reference current stable in temperature.
Another object of the present invention is to realize a reference current circuit that is able to provide a reference current that is stable in temperature in the presence of a low supply voltage.
Yet another object of the present invention is to employ devices implemented only in HCMOS technology, so that it is possible to be realized in a great variety of CMOS processes.
A further object of the present invention is to realize a current reference circuit with low power consumption in all working conditions, independent from the supply voltage.
One embodiment of the present invention provides a current reference circuit for low supply voltages. The current reference circuit includes a series including a resistor and a diode, a current source having one terminal coupled to a supply voltage and another terminal coupled to the series, an operational amplifier having its negative electrode connected to a band gap reference voltage, and a transistor. The diode has its cathode electrode coupled to ground and its anode electrode coupled to the resistor. The transistor has its gate electrode coupled to the output of the operational amplifier, its source electrode coupled to ground, and its drain electrode coupled to both the positive electrode of the operational amplifier and the current source.
Another embodiment of the present invention provides an integrated circuit that includes at least one current reference circuit for low supply voltages.
Yet another embodiment of the present invention provides a signal processing system that includes at least one current reference circuit for low supply voltages.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only and various modifications may naturally be performed without deviating from the present invention.